Tracker alignment in CMS$:$interplay with pixel local reconstruction

TL;DR

This paper discusses the CMS tracker alignment process, emphasizing the importance of precise sensor positioning, the impact of sensor aging on local reconstruction, and the interplay between alignment and pixel calibration.

Contribution

It introduces the CMS alignment procedure and the dedicated calibration for pixel local reconstruction, highlighting how sensor aging affects alignment accuracy.

Findings

Sensor aging impacts pixel hit reconstruction.

Alignment corrections are essential for maintaining tracking precision.

Calibration procedures adapt to sensor response changes over time.

Abstract

The CMS silicon tracking system measures the trajectories of charged particles with a hit resolution of the order of microns in the pixel detector and tens of microns in the strip detector. One of the most important inputs for track reconstruction is the precision with which the tracker geometry is known. Therefore the position, orientation, and curvature of each tracker sensor must be precisely determined. Changes in the operating conditions can cause movements in the different substructures and also in the sensors. For maintaining the targeted precision, frequent corrections are needed, and the procedure to determine these corrections is commonly referred to as tracker alignment. Due to accumulated radiation during data taking, the response of the sensors changes over time. This affects the local reconstruction of pixel hits and consequently the result of the alignment procedure. In this contribution, the alignment procedure in CMS is introduced, as well as the dedicated calibration for the pixel local reconstruction. The effect of the change in the local reconstruction due to aging of the sensors on the alignment procedure is discussed.